Process for plating adherent lead dioxide



United States Patent 3,087,870 PROCESS FOR PLATHNG ADHERENT LEAD DEOXHDE Herman M. Zimmerman, Lakewood, Ohio, assignor to Union Carbide Corporation, a corporation of New York No Drawing. Filed June 22, 1959, Ser. No. 822,715 6 Claims. (Cl. 204--32) This invention relates to a process for plating adherent lead dioxide depolarizers on thin metal strips intended for use as the positive electrode in reserve-type batteries characterized by a high flash current and eificient perform ance at low temperatures.

Heretofore lead dioxide was deposited anodically from aqueous acid solutions of lead nitrate onto base metals such as nickel, stainless steel, terneplate and platinum. The conditions for maximum adherence were unknown, however, and when a plated strip was blanked out in a punch press, the lead dioxide chipped or cracked unpredictably.

The main object of this invention is to provide a process for securely depositing lead dioxide onto a base metal.

Another object of the invention is to provide a novel process for making lead dioxide positive electrodes.

The process in accordance with the present invention and whereby the foregoing objects are attained comprises plating under conditions wherein the base metal, preferably nickel, is actively dissolved anodically, is then suddenly passivated and shifted over to lead dioxide deposition by momentarily applying a greater anode potential or :by lifting the metal strip while still electrically con nected almost entirely from the electrolysis bath, and then slowly replating, after which lead dioxide deposition is continued at a reduced current density.

A modification of this process giving an equivalent product and being more readily susceptible to chemical control and maintenance comprises subjecting a chemically clean and acid-etched nickel or nickel-plated surface to a passivation treatment consisting of a cathodic step and an anodic step in a dilute nitric acid bath followed by the plating of lead dioxide on the metal from nearly neutral lead nitrate solution.

As an example of the practice of the invention, the following typical specification is given:

The base metal was nickel-clad steel. It was electrolytically cleaned in a proprietary alkaline bath and thoroughly rinsed. It was then anodically etched at about 25 amperes per square foot (a.s.f.) for about fifteen seconds in three percent hydrochloric acid and thoroughly rinsed. The following passivation treatment was performed in a three percent nitric acid bath. The cleaned and etched sample was soaked for about eight seconds, during which time it was made cathodic at about 20 a.s.f. if desired.

It was then made anodic at about 80 a.s.f. for about twelve seconds with copious evolution of oxygen from the surface. Anodic treatment was continued for 28 more seconds at 20 a.s.f. The passivated sample Was transferred to a nearly neutral lead nitrate bath (specific gravity 1.300, pH 4.0, temperature 50 C.) and lead 3,087,870 Patented Apr. 30, 1963 dioxide plated anodically at 35 a.s.f. to the thickness desired. Lead cathodes were employed. Additions of lead oxide (PbO) serve to maintain proper pH in this tank.

Relative to the passivation step it has been found that on continuous plating lines, particularly, the cathodic phase of the passivation can be omitted. In batch operations and particularly if for any reason the etch step is omitted, the cathodic portion of the passivation is employed as insurance against deleterious oxide films previously formed.

What is claimed is:

1. A process for electrolytically depositing lead dioxide on a base metal comprising anodically dissolving a porn'on of said metal, passivating said metal in a dilute nitric acid bath by making said metal cathodic and then anodic, placing said metal in a warm, almost neutral lead nitrate bath, and plating lead dioxide anodically onto said metal using a low current density.

2. The process of claim 1 wherein said base metal is nickel-clad steel.

3. A process for electrolytically depositing lead dioxide on a base metal comprising electrolytically cleaning said metal in an alkaline bath, rinsing said cleaned metal, anodically etching said metal in a dilute hydrochloric acid bath, rinsing said metal, passivating said metal in a dilute nitric acid bath, by making said metal cathodic and then anodic, transferring said metal to a nearly neutral Warm lead nitrate bath, and plating lead dioxide anodically onto said metal using a low current density against lead cathodes.

4. The process of claim 3, wherein said base metal is made cathodic for about eight seconds at about 20 amperes per square foot.

5. The process of claim 3 wherein said metal is made anodic for about twelve seconds at about amperes per square foot.

6. The process of claim 3, wherein said nitrate solution has a specific gravity of 1.300 and a pH of 4.

References Cited in the file of this patent UNITED STATES PATENTS 2,571,616 Ruben Oct. 16, 1951 2,711,496 Ruben June 21, 1955 2,846,378 Hoifman Aug. 5, 1958 2,851,405 Dyman et a1. Sept. 9, 1958 2,872,405 Miller et al. Feb. 3, 1959 2,915,444 Meyer Dec. 1, 1959 2,945,790 Grigger July 19, 1960 3,002,900 Henry et a1. Oct. 3, 1961 FOREIGN PATENTS 611,577 Great Britain Nov. 1, 1958 OTHER REFERENCES The Metal Industry (Haas et al.), volume 23, No. 11, November 1925, pages 451 and 452.

Plating (Brune et 211.), September 1955, pages 1127 and 1128. 

1. A PROCESS FOR ELECTROLYTICALLY DEPOSITING LEAD DIOXIDE ON A BASE METAL COMPRISING ANDICALLY DISSOLVING A PORTION OF SAID METAL, PASSIVATING SAID METAL IN A DILUTE NITRIC ACID BATH BY MAKING SAID METAL CATHODIC AND THEN ANODIC, PLACING SAID METAL IN A WARM, ALMOST NEUTRAL LEAD NITRATE BATH, AND PLATING LEAD DIOXIDE ANODICALLY ONTO SAID METAL USING A LOW CURRENT DENSITY. 